Lens Assembly

ABSTRACT

A lens assembly includes a first lens, a second lens, a third lens, and a fourth lens, wherein the first lens, the second lens, the third lens, and the fourth lens are arranged in order from an object side to an image side along an optical axis. The first lens is with positive refractive power and includes a convex surface facing the object side. The second lens is with negative refractive power and includes a concave surface facing the image side. The third lens is with refractive power and includes a convex surface facing the image side. The fourth lens is with refractive power. The lens assembly satisfies: FOV≤56°, wherein FOV is a field of view of the lens assembly.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a lens assembly.

Description of the Related Art

The current development trend of a lens assembly is towardminiaturization. Additionally, the lens assembly is developed to havesmall field of view and high resolution capability in accordance withdifferent application requirements. However, the known lens assemblycan't satisfy such requirements. Therefore, the lens assembly needs anew structure in order to meet the requirements of miniaturization,small field of view, and high resolution at the same time.

BRIEF SUMMARY OF THE INVENTION

The invention provides a lens assembly to solve the above problems. Thelens assembly of the invention is provided with characteristics of ashortened total lens length, a smaller field of view, a higherresolution, and still has a good optical performance.

The lens assembly in accordance with an exemplary embodiment of theinvention includes a first lens, a second lens, a third lens, and afourth lens, wherein the first lens, the second lens, the third lens,and the fourth lens are arranged in order from an object side to animage side along an optical axis. The first lens is with positiverefractive power and includes a convex surface facing the object side.The second lens is with negative refractive power and includes a concavesurface facing the image side. The third lens is with refractive powerand includes a convex surface facing the image side. The fourth lens iswith refractive power. The lens assembly satisfies: FOV≤56°, wherein FOVis a field of view of the lens assembly.

In another exemplary embodiment, the third lens is with negativerefractive power and the fourth lens is with positive refractive power.

In yet another exemplary embodiment, the first lens further includes aconcave surface facing the image side, the second lens further includesa convex surface facing the object side, the third lens further includesa concave surface facing the object side, and the fourth lens includes aconvex surface facing the object side and a concave surface facing theimage side.

In another exemplary embodiment, the first lens further includes aconcave surface facing the image side, the second lens further includesa convex surface facing the object side, the third lens further includesa concave surface facing the object side, and the fourth lens includes aconvex surface facing the object side and a convex surface facing theimage side.

In yet another exemplary embodiment, the lens assembly satisfies:−21.5≤(R₄₁−R₄₂)/(R₄₁+R₄₂), wherein R₄₁ is a radius of curvature of anobject side surface of the fourth lens and R₄₂ is a radius of curvatureof an image side surface of the fourth lens.

In another exemplary embodiment, the lens assembly further includes astop disposed between the object side and the third lens, wherein thelens assembly satisfies: 4 mm<TTL−SL<9 mm, wherein TTL is an intervalfrom the convex surface of the first lens to an image plane along theoptical axis and SL is an interval from the convex surface of the firstlens to the stop along the optical axis.

In yet another exemplary embodiment, the lens assembly satisfies:f₁+f₂<−1 mm, wherein f₁ is an effective focal length of the first lensand f₂ is an effective focal length of the second lens.

In another exemplary embodiment, the lens assembly satisfies: −4≤f₂/f≤0,wherein f₂ is an effective focal length of the second lens and f is aneffective focal length of the lens assembly.

In yet another exemplary embodiment, the lens assembly satisfies:25<V₁−V₂<38, wherein V₁ is an Abbe number of the first lens and V₂ is anAbbe number of the second lens.

In another exemplary embodiment, the lens assembly satisfies: −25mm<f₂+f₄<−1.5 mm, wherein f₂ is an effective focal length of the secondlens and f₄ is an effective focal length of the fourth lens.

The lens assembly in accordance with an exemplary embodiment of theinvention includes a first lens, a second lens, a third lens, a fourthlens, a fifth lens, and a sixth lens, wherein the first lens, the secondlens, the third lens, the fourth lens, the fifth lens, and the sixthlens are arranged in order from an object side to an image side along anoptical axis. The first lens is with positive refractive power andincludes a convex surface facing the object side. The second lens iswith negative refractive power and includes a concave surface facing theimage side. The third lens is with refractive power and includes aconvex surface facing the image side. The fourth lens is with refractivepower. The fifth lens is with refractive power. The sixth lens is withrefractive power. The lens assembly satisfies: 2 mm<f₅+f₆<35 mm, whereinf₅ is an effective focal length of the fifth lens and f₆ is an effectivefocal length of the sixth lens.

In another exemplary embodiment, the third lens is with positiverefractive power, the fourth lens is with negative refractive power, thefifth lens is with positive refractive power, and the sixth lens is withnegative refractive power.

In yet another exemplary embodiment, the second lens further includes aconcave surface facing the object side, the third lens further includesa convex surface facing the object side, the fourth lens is a biconcavelens, the fifth lens includes a convex surface facing the object side,and the sixth lens is a biconcave lens.

In another exemplary embodiment, the second lens further includes aconcave surface facing the object side, the third lens further includesa convex surface facing the object side, the fourth lens is a biconcavelens, the fifth lens includes a concave surface facing the object side,and the sixth lens is a biconcave lens.

In yet another exemplary embodiment, the lens assembly satisfies:−21.5≤(R₄₁−R₄₂)/(R₄₁+R₄₂)≤3.5, wherein R₄₁ is a radius of curvature ofan object side surface of the fourth lens and R₄₂ is a radius ofcurvature of an image side surface of the fourth lens.

In another exemplary embodiment, the lens assembly further includes astop disposed between the object side and the third lens, wherein thelens assembly satisfies: 4 mm<TTL−SL<9 mm, wherein TTL is an intervalfrom the convex surface of the first lens to an image plane along theoptical axis and SL is an interval from the convex surface of the firstlens to the stop along the optical axis.

In yet another exemplary embodiment, the lens assembly satisfies:f₁+f₂<−1 mm, wherein f₁ is an effective focal length of the first lensand f₂ is an effective focal length of the second lens.

In another exemplary embodiment, the lens assembly satisfies: −4≤f₂/f≤0,wherein f₂ is an effective focal length of the second lens and f is aneffective focal length of the lens assembly.

In yet another exemplary embodiment, the lens assembly satisfies:25<V₁−V₂<38, wherein V₁ is an Abbe number of the first lens and V₂ is anAbbe number of the second lens.

In another exemplary embodiment, the lens assembly satisfies: −25mm<f₂+f₄<−1.5 mm, wherein f₂ is an effective focal length of the secondlens and f₄ is an effective focal length of the fourth lens.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a lens layout and optical path diagram of a lens assembly inaccordance with a first embodiment of the invention;

FIG. 2A depicts a longitudinal spherical aberration of the lens assemblyin accordance with the first embodiment of the invention;

FIG. 2B is an astigmatic field curves diagram of the lens assembly inaccordance with the first embodiment of the invention;

FIG. 2C is a distortion diagram of the lens assembly in accordance withthe first embodiment of the invention;

FIG. 3 is a lens layout and optical path diagram of a lens assembly inaccordance with a second embodiment of the invention;

FIG. 4A depicts a longitudinal spherical aberration of the lens assemblyin accordance with the second embodiment of the invention;

FIG. 4B is an astigmatic field curves diagram of the lens assembly inaccordance with the second embodiment of the invention;

FIG. 4C is a distortion diagram of the lens assembly in accordance withthe second embodiment of the invention;

FIG. 5 is a lens layout and optical path diagram of a lens assembly inaccordance with a third embodiment of the invention;

FIG. 6A depicts a field curvature diagram of the lens assembly inaccordance with the third embodiment of the invention;

FIG. 6B is a distortion diagram of the lens assembly in accordance withthe third embodiment of the invention;

FIG. 6C is a modulation transfer function diagram of the lens assemblyin accordance with the third embodiment of the invention;

FIG. 7 is a lens layout and optical path diagram of a lens assembly inaccordance with a fourth embodiment of the invention;

FIG. 8A depicts a field curvature diagram of the lens assembly inaccordance with the fourth embodiment of the invention;

FIG. 8B is a distortion diagram of the lens assembly in accordance withthe fourth embodiment of the invention;

FIG. 8C is a modulation transfer function diagram of the lens assemblyin accordance with the fourth embodiment of the invention;

FIG. 9 is a lens layout and optical path diagram of a lens assembly inaccordance with a fifth embodiment of the invention;

FIG. 10A depicts a field curvature diagram of the lens assembly inaccordance with the fifth embodiment of the invention;

FIG. 10B is a distortion diagram of the lens assembly in accordance withthe fifth embodiment of the invention; and

FIG. 10C is a modulation transfer function diagram of the lens assemblyin accordance with the fifth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is made for the purpose of illustrating thegeneral principles of the invention and should not be taken in alimiting sense. The scope of the invention is best determined byreference to the appended claims.

Referring to FIG. 1, FIG. 1 is a lens layout and optical path diagram ofa lens assembly in accordance with a first embodiment of the invention.The lens assembly 1 includes a stop ST1, a first lens L11, a second lensL12, a third lens L13, a fourth lens L14, an optical filter OF1, and acover glass CG1, all of which are arranged in order from an object sideto an image side along an optical axis OA1. In operation, an image oflight rays from the object side is formed at an image plane IMA1.

The first lens L11 is a meniscus lens with positive refractive power andmade of glass material, wherein the object side surface S12 is a convexsurface, the image side surface S13 is a concave surface, and both ofthe object side surface S12 and image side surface S13 are asphericsurfaces.

The second lens L12 is a meniscus lens with negative refractive powerand made of plastic material, wherein the object side surface S14 is aconvex surface, the image side surface S15 is a concave surface, andboth of the object side surface S14 and image side surface S15 areaspheric surfaces.

The third lens L13 is a meniscus lens with negative refractive power andmade of plastic material, wherein the object side surface S16 is aconcave surface, the image side surface S17 is a convex surface, andboth of the object side surface S16 and image side surface S17 areaspheric surfaces.

The fourth lens L14 is a meniscus lens with positive refractive powerand made of plastic material, wherein the object side surface S18 is aconvex surface, the image side surface S19 is a concave surface, andboth of the object side surface S18 and image side surface S19 areaspheric surfaces.

Both of the object side surface S110 and image side surface S111 of theoptical filter OF1 are plane surfaces.

Both of the object side surface S112 and image side surface S113 of thecover glass CG1 are plane surfaces.

In order to maintain excellent optical performance of the lens assemblyin accordance with the first embodiment of the invention, the lensassembly 1 satisfies at least one of the following conditions:

FOV1≤56°  (1)

4 mm<TTL1−SL1<9 mm   (2)

f1₁ +f1₂<−1 mm   (3)

−4≤f1₂ /f1≤0   (4)

25<V1₁ −V1₂<38   (5)

−21.5≤(R1₄₁ −R1₄₂)/(R1₄₁ +R1₄₂)≤3.5   (6)

−25 mm<f1₂ +f1₄<−1.5 mm   (7)

wherein FOV1 is a field of view in degree for the lens assembly 1, TTL1is an interval from the object side surface S12 of the first lens L11 tothe image plane IMA1 along the optical axis OA1, SL1 is an interval fromthe object side surface S12 of the first lens L11 to the stop ST1 alongthe optical axis OA1, f1 ₁ is an effective focal length of the firstlens L11, f1 ₂ is an effective focal length of the second lens L12, f1 ₄is an effective focal length of the fourth lens L14, f1 is an effectivefocal length of the lens assembly 1, V1 ₁ is an Abbe number of the firstlens L11, V1 ₂ is an Abbe number of the second lens L12, R1 ₄₁ is aradius of curvature of the object side surface S18 of the fourth lensL14, and R1 ₄₂ is a radius of curvature of the image side surface S19 ofthe fourth lens L14.

By the above design of the lenses, stop ST1, and satisfies at least oneof the conditions (1)-(7), the lens assembly 1 is provided with aneffective shortened total lens length, an effective decreased field ofview, an increased resolution, and an effective corrected aberration.

In order to achieve the above purposes and effectively enhance theoptical performance, the lens assembly 1 in accordance with the firstembodiment of the invention is provided with the optical specificationsshown in Table 1, which include the effective focal length, F-number,total lens length, field of view, radius of curvature of each lenssurface, thickness between adjacent surface, refractive index of eachlens, Abbe number of each lens, and effective focal length of each lens.Table 1 shows that the effective focal length is equal to 5.4619 mm,F-number is equal to 4.5, total lens length is equal to 6.688 mm, andfield of view is equal to 43.9779 degrees for the lens assembly 1 of thefirst embodiment of the invention.

TABLE 1 Effective Focal Length = 5.4619 mm F-number = 4.5 Total LensLength = 6.688 mm Field of View = 43.9779 Degrees Radius of EffectiveSurface Curvature Thickness Focal Length Number (mm) (mm) Nd Vd (mm)Remark S11 ∞ 0.000 Stop ST1 S12 1.852 0.395 1.589 61.2 3.51310 The FirstLens L11 S13 16.186 0.050 S14 2.591 0.500 1.636 23.9 −6.02370 The SecondLens L12 S15 1.429 1.578 S16 −0.853 0.500 1.636 23.9 −5.11500 The ThirdLens L13 S17 −1.420 0.050 S18 2.103 1.030 1.535 55.7 4.1985 The FourthLens L14 S19 27.234 0.500 S110 ∞ 0.210 1.517 64.2 Optical Filter OF1S111 ∞ 1.426 S112 ∞ 0.400 1.517 64.2 Cover Glass CG1 S113 ∞ 0.050

The aspheric surface sag z of each lens in table 1 can be calculated bythe following formula:

z=ch ²/{1+[1−(k+1)c ² h ²]^(1/2) }+Ah ⁴ +Bh ⁶ +Ch ⁸ +Dh ¹⁰

where c is curvature, h is the vertical distance from the lens surfaceto the optical axis, k is conic constant and A, B, C and D are asphericcoefficients.

In the first embodiment, the conic constant k and the asphericcoefficients A, B, C, D of each surface are shown in Table 2.

TABLE 2 Surface Number S12 S13 S14 S15 K −3.5527E−01   0.0000E+00−1.6190E+00 −2.9888E−02 A   3.8319E−03 −8.7036E−03 −2.2288E−03−5.4284E−02 B −4.7768E−03   1.7903E−05   6.5077E−03   6.2554E−03 C  0.0000E+00   6.5897E−03   1.1869E−04   8.6668E−03 D   0.0000E+00  0.0000E+00   7.0890E−05   9.8377E−03 Surface Number S16 S17 S18 S19 K−2.3851E+00 −2.1665E+00 −9.4074E+00   0.0000E+00 A −5.1997E−02−1.2031E−02 −1.1391E−02 −2.9667E−02 B −2.0059E−02   2.2708E−03  4.4922E−03   3.3095E−03 C   3.5820E−02   5.3712E−03 −1.0136E−03  6.4504E−04 D −1.7535E−02 −2.0000E−03   1.1801E−04 −1.1033E−04

Table 3 shows the parameters and condition values for conditions(1)-(7). As can be seen from Table 3, the lens assembly 1 of the firstembodiment satisfies the conditions (1)-(7).

TABLE 3 FOV1 43.9779 TTL1  6.688 mm SL 1 0 mm Degrees f1₁ 3.5131 mm f1₂−6.02370 f1₄ 4.1985 mm mm f1 5.4619 mm V1₁ 61.2 V1₂ 23.9 R1₄₁  2.103 mmR1₄₂ 27.234 mm FOV1 43.9779 TTL1 − SL1  6.688 mm f1₁ + f1₂ −2.511Degrees mm f1₂ + f1₄ −1.825 mm f1₂/f1 −1.103 V1₁ − V1₂ 37.3 (R1₄₁ −R1₄₂)/( R1₄₁ + R1₄₂) −0.857

By the above arrangements of the lenses and stop ST1, the lens assembly1 of the first embodiment can meet the requirements of opticalperformance as seen in FIGS. 2A-2C, wherein FIG. 2A shows a longitudinalspherical aberration diagram of the lens assembly 1 in accordance withthe first embodiment of the invention, FIG. 2B shows an astigmatic fieldcurves diagram of the lens assembly 1 in accordance with the firstembodiment of the invention, and FIG. 2C shows a distortion diagram ofthe lens assembly 1 in accordance with the first embodiment of theinvention.

It can be seen from FIG. 2A that the longitudinal spherical aberrationin the lens assembly 1 of the first embodiment ranges from −0.005 mm to0.013 mm for the wavelength of 435.8300 nm, 546.0700 nm, and 656.2800nm.

It can be seen from FIG. 2B that the astigmatic field curves oftangential direction and sagittal direction in the lens assembly 1 ofthe first embodiment ranges from −0.005 mm to 0.005 mm for thewavelength of 546.0700 nm.

It can be seen from FIG. 2C that the distortion in the lens assembly 1of the first embodiment ranges from 0% to 0.5% for the wavelength of546.0700 nm.

It is obvious that the longitudinal spherical aberration, the astigmaticfield curves, and the distortion of the lens assembly 1 of the firstembodiment can be corrected effectively. Therefore, the lens assembly 1of the first embodiment is capable of good optical performance.

Referring to FIG. 3, FIG. 3 is a lens layout and optical path diagram ofa lens assembly in accordance with a second embodiment of the invention.The lens assembly 2 includes a stop ST2, a first lens L21, a second lensL22, a third lens L23, a fourth lens L24, an optical filter OF2, and acover glass CG2, all of which are arranged in order from an object sideto an image side along an optical axis OA2. In operation, an image oflight rays from the object side is formed at an image plane IMA2.

The first lens L21 is a meniscus lens with positive refractive power andmade of glass material, wherein the object side surface S22 is a convexsurface, the image side surface S23 is a concave surface, and both ofthe object side surface S22 and image side surface S23 are asphericsurfaces.

The second lens L22 is a meniscus lens with negative refractive powerand made of plastic material, wherein the object side surface S24 is aconvex surface, the image side surface S25 is a concave surface, andboth of the object side surface S24 and image side surface S25 areaspheric surfaces.

The third lens L23 is a meniscus lens with negative refractive power andmade of plastic material, wherein the object side surface S26 is aconcave surface, the image side surface S27 is a convex surface, andboth of the object side surface S26 and image side surface S27 areaspheric surfaces.

The fourth lens L24 is a biconvex lens with positive refractive powerand made of plastic material, wherein the object side surface S28 is aconvex surface, the image side surface S29 is a convex surface, and bothof the object side surface S28 and image side surface S29 are asphericsurfaces.

Both of the object side surface S210 and image side surface S211 of theoptical filter OF2 are plane surfaces.

Both of the object side surface S212 and image side surface S213 of thecover glass CG2 are plane surfaces.

In order to maintain excellent optical performance of the lens assemblyin accordance with the second embodiment of the invention, the lensassembly 2 satisfies at least one of the following conditions:

FOV2≤56°  (8)

4 mm<TTL2−SL2<9 mm   (9)

f2₁ +f2₂<−1 mm   (10)

−4≤f2₂ /f2≤0   (11)

25<V2₁ −V2₂<38   (12)

−21.5≤(R2₄₁ −R2₄₂)/(R2₄₁ +R2₄₂)≤3.5   (13)

−25 mm<f2₂ +f2₄<−1.5 mm   (14)

The definition of FOV2, TTL2, SL2, f2 ₁, f2 ₂, f2 ₄, f2, V2 ₁, V2 ₂, R2₄₁, and R2 ₄₂ are the same as that of FOV1, TTL1, SL1, f1 ₁, f1 ₂, f1 ₄,f1, V1 ₁, V1 ₂, R1 ₄₁, and R1 ₄₂ in the first embodiment, and is notdescribed here again.

By the above design of the lenses, stop ST2, and satisfies at least oneof the conditions (8)-(14), the lens assembly 2 is provided with aneffective shortened total lens length, an effective decreased field ofview, an increased resolution, and an effective corrected aberration.

In order to achieve the above purposes and effectively enhance theoptical performance, the lens assembly 2 in accordance with the secondembodiment of the invention is provided with the optical specificationsshown in Table 4, which include the effective focal length, F-number,total lens length, field of view, radius of curvature of each lenssurface, thickness between adjacent surface, refractive index of eachlens, Abbe number of each lens, and effective focal length of each lens.Table 4 shows that the effective focal length is equal to 5.4246 mm,F-number is equal to 4.5, total lens length is equal to 7.412 mm, andfield of view is equal to 44.0706 degrees for the lens assembly 2 of thesecond embodiment of the invention.

TABLE 4 Effective Focal Length = 5.4246 mm F-number = 4.5 Total LensLength = 7.412 mm Field of View = 44.0706 Degrees Sur- Effective faceRadius of Thick- Focal Num- Curvature ness Length ber (mm) (mm) Nd Vd(mm) Remark S21 ∞ −0.090 Stop ST2 S22 2.066 0.500 1.589 61.2 5.59480 TheFirst Lens S23 5.037 0.453 L21 S24 2.097 0.300 1.636 23.9 −19.03600 TheSecond Lens L22 S25 1.688 0.682 S26 −0.635 0.300 1.636 23.9 −3.00140 TheThird Lens S27 −1.126 0.100 L23 S28 2.442 1.006 1.535 55.7 2.8826 TheFourth Lens L24 S29 −3.585 0.500 S210 ∞ 0.210 1.517 64.2 Optical FilterS211 ∞ 3.001 OF2 S212 ∞ 0.400 1.517 Cover Glass CG2 S213 ∞ 0.050

The aspheric surface sag z of each lens in table 4 can be calculated bythe following formula:

z=ch ²/{1+[1−(k+1)c ² h ²]^(1/2) }+Ah ⁴ +Bh ⁶ +Ch ⁸ +Dh ¹⁰

where c is curvature, h is the vertical distance from the lens surfaceto the optical axis, k is conic constant and A, B, C and D are asphericcoefficients.

In the second embodiment, the conic constant k and the asphericcoefficients A, B, C, D of each surface are shown in Table 5.

TABLE 5 Surface Number S22 S23 S24 S25 K   3.0921E−03   0.0000E+00−6.3202E+00 −1.8255E+00 A   6.7904E−03 −2.4248E−02 −1.2011E−02−3.9700E−02 B −4.9964E−03 −2.4752E−03 −3.8126E−02   2.6612E−02 C−1.5750E−04 −1.6603E−02   9.0336E−03   2.3417E−03 D   0.0000E+00  0.0000E+00 −3.5095E−03 −1.2144E−03 Surface Number S26 S27 S28 S29 K−2.1224E+00 −2.8806E+00 −2.2729E+01   0.0000E+00 A −5.2106E−02  1.4819E−02 −1.7987E−02 −8.0327E−03 B   1.6977E−02   7.5686E−03  6.6630E−03   1.0811E−03 C   6.4081E−02   2.5693E−03 −2.7596E−03−7.5699E−04 D −1.5156E−02 −3.5407E−03 −5.3512E−04 −7.3260E−05

Table 6 shows the parameters and condition values for conditions(8)-(14). As can be seen from Table 6, the lens assembly 2 of the secondembodiment satisfies the conditions (8)-(14).

TABLE 6 FOV2 44.0706 TTL2   7.412 mm SL2 0.09 mm Degrees f2₁ 5.5948 mmf2₂ −19.03600 f2₄ 2.8826 mm mm f2 5.4246 mm V2₁ 61.2 V2₂ 23.9 R2₄₁ 2.442 mm R2₄₂ −3.582 mm FOV2 44.0706 TTL2 − SL2   7.322 mm f2₁ + f2₂−13.4412 Degrees mm f2₂ + f2₄ −16.153 f2₂/f2 −3.509 V2₁ − V2₂ 37.3 mm(R2₄₁ − R2₄₂)/( R2₄₁ + R2₄₂) −5.274

By the above arrangements of the lenses and stop ST2, the lens assembly2 of the second embodiment can meet the requirements of opticalperformance as seen in FIGS. 4A-4C, wherein FIG. 4A shows a longitudinalspherical aberration diagram of the lens assembly 2 in accordance withthe second embodiment of the invention, FIG. 4B shows an astigmaticfield curves diagram of the lens assembly 2 in accordance with thesecond embodiment of the invention, and FIG. 4C shows a distortiondiagram of the lens assembly 2 in accordance with the second embodimentof the invention.

It can be seen from FIG. 4A that the longitudinal spherical aberrationin the lens assembly 2 of the second embodiment ranges from 0.00 mm to0.030 mm for the wavelength of 435.8300 nm, 546.0700 nm, and 656.2800nm.

It can be seen from FIG. 4B that the astigmatic field curves oftangential direction and sagittal direction in the lens assembly 2 ofthe second embodiment ranges from −0.015 mm to 0.018 mm for thewavelength of 546.0700 nm.

It can be seen from FIG. 4C that the distortion in the lens assembly 2of the second embodiment ranges from 0% to 1.3% for the wavelength of546.0700 nm.

It is obvious that the longitudinal spherical aberration, the astigmaticfield curves, and the distortion of the lens assembly 2 of the secondembodiment can be corrected effectively. Therefore, the lens assembly 2of the second embodiment is capable of good optical performance.

Referring to FIG. 5, FIG. 5 is a lens layout and optical path diagram ofa lens assembly in accordance with a third embodiment of the invention.The lens assembly 3 includes a stop ST3, a first lens L31, a second lensL32, a third lens L33, a fourth lens L34, a fifth lens L35, a sixth lensL36, and an optical filter OF3, all of which are arranged in order froman object side to an image side along an optical axis OA3. In operation,an image of light rays from the object side is formed at an image planeIMA3.

The first lens L31 is a meniscus lens with positive refractive power andmade of plastic material, wherein the object side surface S32 is aconvex surface, the image side surface S33 is a concave surface, andboth of the object side surface S32 and image side surface S33 areaspheric surfaces.

The second lens L32 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S34 is aconcave surface, the image side surface S35 is a concave surface, andboth of the object side surface S34 and image side surface S35 areaspheric surfaces.

The third lens L33 is a biconvex lens with positive refractive power andmade of plastic material, wherein the object side surface S36 is aconvex surface, the image side surface S37 is a convex surface, and bothof the object side surface S36 and image side surface S37 are asphericsurfaces.

The fourth lens L34 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S38 is aconcave surface, the image side surface S39 is a concave surface, andboth of the object side surface S38 and image side surface S39 areaspheric surfaces.

The fifth lens L35 is a biconvex lens with positive refractive power andmade of plastic material, wherein the object side surface S310 is aconvex surface, the image side surface S311 is a convex surface, andboth of the object side surface S310 and image side surface S311 areaspheric surfaces.

The sixth lens L36 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S312 is aconcave surface, the image side surface S313 is a concave surface, andboth of the object side surface S312 and image side surface S313 areaspheric surfaces

Both of the object side surface S314 and image side surface S315 of theoptical filter OF3 are plane surfaces.

In order to maintain excellent optical performance of the lens assemblyin accordance with the third embodiment of the invention, the lensassembly 3 satisfies at least one of the following conditions:

FOV3≤56°  (15)

4 mm<TTL3−SL3<9 mm   (16)

f3₁ −f3₂<−1 mm   (17)

−25 mm<f3₂ +f3₄<−1.5 mm   (18)

−4≤f3₂ /f3≤0   (19)

2 mm<f3₅ +f3₆<35 mm   (20)

25<V3₁ −V3₂<38   (21)

−21.5≤(R3₄₁ −R3₄₂)/(R3₄₁ +R3₄₂)≤3.5   (22)

The definition of FOV3, TTL3, SL3, f3 ₁, f3 ₂, f3 ₄, f3, V3 ₁, V3 ₂, R3₄₁, and R3 ₄₂ are the same as that of FOV1, TTL1, SL1, f1 ₁, f1 ₂, f1 ₄,f1, V1 ₁, V1 ₂, R1 ₄₁, and R1 ₄₂ in the first embodiment, and is notdescribed here again. f3 ₅ is an effective focal length of the fifthlens L35 and f3 ₆ is an effective focal length of the sixth lens L36.

By the above design of the lenses, stop ST3, and satisfies at least oneof the conditions (15)-(22), the lens assembly 3 is provided with aneffective shortened total lens length, an effective decreased field ofview, an increased resolution, and an effective corrected aberration.

In order to achieve the above purposes and effectively enhance theoptical performance, the lens assembly 3 in accordance with the thirdembodiment of the invention is provided with the optical specificationsshown in Table 7, which include the effective focal length, F-number,total lens length, field of view, radius of curvature of each lenssurface, thickness between adjacent surface, refractive index of eachlens, Abbe number of each lens, and effective focal length of each lens.Table 7 shows that the effective focal length is equal to 5.574 mm,F-number is equal to 2.8, total lens length is equal to 5.88 mm, andfield of view is equal to 55.5 degrees for the lens assembly 3 of thethird embodiment of the invention.

TABLE 7 Effective Focal Length = 5.574 mm F-number = 2.8 Total LensLength = 5.88 mm Field of View = 55.5 Degrees Radius of EffectiveSurface Curvature Thickness Focal Length Number (mm) (mm) Nd Vd (mm)Remark S31 ∞ −0.316 Stop ST3 S32 1.7608 0.591 1.535 56.115 3.423 TheFirst Lens L31 S33 38.585 0.026 S34 −2512.54 0.35 1.636 23.972 −6.364The Second Lens L32 S35 4.064 0.6 S36 8.398 1.083 1.535 56.115 7.624 TheThird Lens L33 S37 −7.599 0.159 S38 −5.616 0.266 1.544 56.093 −5.354 TheFourth Lens L34 S39 6.171 0.031 S310 4.21 0.777 1.535 56.115 6.588 TheFifth Lens L35 S311 −20.468 0.791 S312 −3.319 0.295 1.535 56.115 −3.847The Sixth Lens L36 S313 5.609 0.345 S314 ∞ 0.21 1.517 64.167 OpticalFilter OF3 S315 ∞ 0.396

The aspheric surface sag z of each lens in table 7 can be calculated bythe following formula:

z=ch ²/{1+[1−(k+1)c ² h ²]^(1/2) }+Ah ⁴ +Bh ⁶ +Ch ⁸ +Dh ¹⁰ +Eh ¹² +Fh ¹⁴+Gh ¹⁶

where c is curvature, h is the vertical distance from the lens surfaceto the optical axis, k is conic constant and A, B, C, D, E, F and G areaspheric coefficients.

In the third embodiment, the conic constant k and the asphericcoefficients A, B, C, D, E, F, G of each surface are shown in Table 8.

TABLE 8 Surface k A B C Number D E F G S32 0.024   8.24E−03 −4.99E−03  8.59E−03 −4.32E−03 −4.69E−04 −2.01E−03 −1.12E−03 S33 0 −8.55E−03  8.54E−03   8.86E−03   1.05E−02 −1.84E−04 −2.31E−03 −1.12E−02 S34 0−2.40E−02   2.59E−02   2.08E−02   1.46E−02 −8.56E−03 −5.08E−03 −1.09E−03S35 −1.101 −9.52E−03   5.91E−02 −7.41E−03   3.23E−02 −1.01E−02 −2.66E−02  3.80E−02 S36 3.316 −3.62E−02 −1.80E−03   7.05E−03   1.08E−02 −5.64E−03−1.37E−02   7.73E−03 S37 0 −1.12E−01   1.07E−02 −2.49E−02 −7.59E−03  8.03E−03   7.83E−03 −6.23E−03 S38 0 −5.86E−02 −2.50E−02 −9.50E−03−5.81E−03 −3.53E−03 −1.59E−03   1.41E−03 S39 −0.904 −3.41E−02   1.26E−02  1.38E−03 −2.64E−03 −1.61E−03 −6.45E−04 −2.98E−04 S310 4.469 −6.85E−02  1.93E−02 −1.29E−02   1.03E−03   8.80E−04 −3.64E−04 −1.23E−08 S311−1002.23   3.17E−02   6.87E−04 −3.47E−03 −5.00E−04   4.84E−05   1.45E−04−2.39E−05 S312 1.759 −3.46E−02   4.98E−04   9.89E−03 −7.83E−04 −7.24E−04−4.02E−05   4.00E−05 S313 −10.386 −6.64E−02   1.42E−02 −2.36E−03  2.26E−04 −1.74E−05 −5.58E−06   4.41E−07

Table 9 shows the parameters and condition values for conditions(15)-(22). As can be seen from Table 8, the lens assembly 3 of the thirdembodiment satisfies the conditions (15)-(22).

TABLE 9 FOV3 55.5 TTL3 5.88 mm SL3 0.316 Degrees mm f3₁    3.423 mm f3₂−6.364 f3₄ −5.354 mm mm f3₅    6.588 mm f3₆ −3.847 f3   5.574 mm mm V3₁56.115 V3₂ 23.972 R3₄₁ −5.616 mm R3₄₂    6.171 mm FOV3 55.5 TTL3 − SL35.564 f3₁ + f3₂ −2.941 Degrees mm mm f3₂ + f3₄ −11.718 mm f3₂/f3 −1.142f3₅ + f3₆   2.741 mm V3₁ − V3₂ 32.143 (R3₄₁ − R3₄₂)/(R3₄₁ + R3₄₂)−21.238

By the above arrangements of the lenses and stop ST3, the lens assembly3 of the third embodiment can meet the requirements of opticalperformance as seen in FIGS. 6A-6C, wherein FIG. 6A shows a fieldcurvature diagram of the lens assembly 3 in accordance with the thirdembodiment of the invention, FIG. 6B shows a distortion diagram of thelens assembly 3 in accordance with the third embodiment of theinvention, and FIG. 6C shows a modulation transfer function diagram ofthe lens assembly 3 in accordance with the third embodiment of theinvention.

It can be seen from FIG. 6A that the field curvature of tangentialdirection and sagittal direction in the lens assembly 3 of the thirdembodiment ranges from −0.06 mm to 0.05 mm for the wavelength of 0.439μm, 0.546 μm, 0.573 μm, 0.587 μm, and 0.656 μm.

It can be seen from FIG. 6B that the distortion in the lens assembly 3of the third embodiment ranges from 0% to 1.8% for the wavelength of0.439 μm, 0.546 μm, 0.573 μm, 0.587 μm, and 0.656 μm.

It can be seen from FIG. 6C that the modulation transfer function oftangential direction and sagittal direction in the lens assembly 3 ofthe third embodiment ranges from 0.38 to 1.0 wherein the wavelengthranges from 0.4385 μm to 0.6563 μm, the fields respectively are 0.0000mm, 0.5867 mm, 1.1734 mm, 1.4668 mm, 2.0535 mm, 2.6402 mm, and 2.9335mm, and the spatial frequency ranges from 0 lp/mm to 125 lp/mm.

It is obvious that the field curvature and the distortion of the lensassembly 3 of the third embodiment can be corrected effectively, and theresolution of the lens assembly 3 of the third embodiment can meet therequirement. Therefore, the lens assembly 3 of the third embodiment iscapable of good optical performance.

Referring to FIG. 7, FIG. 7 is a lens layout and optical path diagram ofa lens assembly in accordance with a fourth embodiment of the invention.The lens assembly 4 includes a first lens L41, a stop ST4, a second lensL42, a third lens L43, a fourth lens L44, a fifth lens L45, a sixth lensL46, and an optical filter OF4, all of which are arranged in order froman object side to an image side along an optical axis OA4. In operation,an image of light rays from the object side is formed at an image planeIMA4.

The first lens L41 is a meniscus lens with positive refractive power andmade of plastic material, wherein the object side surface S41 is aconvex surface, the image side surface S42 is a concave surface, andboth of the object side surface S41 and image side surface S42 areaspheric surfaces.

The second lens L42 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S43 is aconcave surface, the image side surface S44 is a concave surface, andboth of the object side surface S43 and image side surface S44 areaspheric surfaces.

The third lens L43 is a biconvex lens with positive refractive power andmade of plastic material, wherein the object side surface S45 is aconvex surface, the image side surface S46 is a convex surface, and bothof the object side surface S45 and image side surface S46 are asphericsurfaces.

The fourth lens L44 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S47 is aconcave surface, the image side surface S48 is a concave surface, andboth of the object side surface S47 and image side surface S48 areaspheric surfaces.

The fifth lens L45 is a meniscus lens with positive refractive power andmade of plastic material, wherein the object side surface S49 is aconvex surface, the image side surface S410 is a concave surface, andboth of the object side surface S49 and image side surface S410 areaspheric surfaces.

The sixth lens L46 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S411 is aconcave surface, the image side surface S412 is a concave surface, andboth of the object side surface S411 and image side surface S412 areaspheric surfaces

Both of the object side surface S413 and image side surface S414 of theoptical filter OF4 are plane surfaces.

In order to maintain excellent optical performance of the lens assemblyin accordance with the fourth embodiment of the invention, the lensassembly 4 satisfies at least one of the following conditions:

FOV4≤56°  (23)

4 mm<TTL4−SL4<9 mm   (24)

f4₁ +f4₂<−1 mm   (25)

−25 mm<f4₂ +f4₄<−1.5 mm   (26)

−4≤f4₂ /f4≤0   (27)

2 mm<f4₅ +f4₆<35 mm   (28)

25<V4₁ −V4₂<38   (29)

−21.5≤(R4₄₁ −R4₄₂)/(R4₄₁ +R4₄₂)≤3.5   (30)

The definition of FOV4, TTL4, SL4, f4 ₁, f4 ₂, f4 ₄, f4 ₅, f4 ₆, f4, V4₁, V4 ₂, R4 ₄₁, and R4 ₄₂ are the same as that of FOV3, TTL3, SL3, f3 ₁,f3 ₂, f³ ₄, f3 ₅, f3 ₆, f3, V3 ₁, V3 ₂, R3 ₄₁, and R3 ₄₂ in the thirdembodiment, and is not described here again.

By the above design of the lenses, stop ST4, and satisfies at least oneof the conditions (23)-(30), the lens assembly 4 is provided with aneffective shortened total lens length, an effective decreased field ofview, an increased resolution, and an effective corrected aberration.

In order to achieve the above purposes and effectively enhance theoptical performance, the lens assembly 4 in accordance with the fourthembodiment of the invention is provided with the optical specificationsshown in Table 10, which include the effective focal length, F-number,total lens length, field of view, radius of curvature of each lenssurface, thickness between adjacent surface, refractive index of eachlens, Abbe number of each lens, and effective focal length of each lens.Table 10 shows that the effective focal length is equal to 7.082 mm,F-number is equal to 2.8, total lens length is equal to 7.7 mm, andfield of view is equal to 45 degrees for the lens assembly 4 of thefourth embodiment of the invention.

TABLE 10 Effective Focal Length = 7.082 mm F-number = 2.8 Total LensLength = 7.7 mm Field of View = 45 Degrees Radius of Effective FocalSurface Curvature Thickness Length Number (mm) (mm) Nd Vd (mm) RemarkS41 2.347197 0.910177 1.535 56.115 4.547 The First Lens L41 S42 54.938090.046326 Stop ST4 S43 −20.1212 0.249992 1.636 23.972 −7.392 The SecondLens L42 S44 6.184075 0.108445 S45 7.374668 1.184192 1.535 56.115 9.335The Third Lens L43 S46 −14.6877 0.274388 S47 −11.0451 0.913223 1.54456.093 −6.845 The Fourth Lens L44 S48 5.799714 0.02497 S49 4.3048541.69802 1.535 56.115 9.369 The Fifth Lens L45 S410 26.00662 1.176473S411 −3.46793 0.309922 1.535 56.115 −4.533 The Sixth Lens L46 S4128.369748 0.4 S413 ∞ 0.21 1.517 64.167 Optical Filter OF4 S414 ∞ 0.195235

The aspheric surface sag z of each lens in table 10 can be calculated bythe following formula:

z=ch ²/{1+[1−(k+1)c ² h ²]^(1/2) }+Ah ⁴ +Bh ⁶ +Ch ⁸ +Dh ¹⁰ +Eh ¹² +Fh ¹⁴+Gh ¹⁶

where c is curvature, h is the vertical distance from the lens surfaceto the optical axis, k is conic constant and A, B, C, D, E, F and G areaspheric coefficients.

In the fourth embodiment, the conic constant k and the asphericcoefficients A, B, C, D, E, F, G of each surface are shown in Table 11.

TABLE 11 Surface k A B C Number D E F G S41 0.024   1.76E−03 −3.29E−03  5.27E−03 −3.55E−03 −1.46E−03   1.76E−03 −4.44E−04 S42 0   2.24E−02  4.43E−03 −4.83E−03   6.44E−03   1.79E−04 −3.88E−03   2.56E−04 S43 0  9.51E−03   1.78E−02   1.17E−02 −2.62E−03 −4.35E−03   1.77E−03−1.16E−03 S44 −1.101 −1.02E−02   5.70E−02 −1.67E−03   1.29E−02 −5.04E−03−1.22E−02   5.30E−03 S45 3.316 −1.12E−02   1.43E−02   2.27E−02 −1.14E−02−9.35E−03   4.35E−03 −2.56E−03 S46 0 −1.14E−01   4.02E−03 −3.38E−03−2.41E−03 −1.00E−03   5.70E−03 −3.28E−03 S47 0 −1.66E−01 −1.16E−02  3.32E−02 −4.85E−03 −1.50E−02   9.61E−03 −4.51E−04 S48 −0.904 −3.12E−02  2.29E−02   1.67E−03 −4.93E−03 −8.00E−04   1.21E−03 −1.43E−04 S49 4.469  1.05E−02   1.80E−03 −4.87E−03 −7.58E−04   8.69E−05   3.40E−04−9.80E−05 S410 −1002.23   2.79E−02 −4.18E−03   1.76E−03 −3.52E−04−6.09E−05   2.60E−05 −1.55E−06 S411 1.759 −7.58E−02   2.53E−02 −3.34E−04−1.07E−03 −9.58E−05   2.59E−05   1.15E−05 S412 −10.386 −5.33E−02  1.12E−02 −4.96E−04 −2.72E−04   3.17E−07   7.68E−06 −5.92E−07

Table 12 shows the parameters and condition values for conditions(23)-(30). As can be seen from Table 12, the lens assembly 4 of thefourth embodiment satisfies the conditions (23)-(30).

TABLE 12 FOV4 45 TTL4  7.7 mm SL4 0.910 Degrees mm f4₁ 4.547 mm f4₂−7.392 f4₄ −6.845 mm mm f4₅ 9.369 mm f4₆ −4.533 f4 7.082 mm mm V4₁56.115 V4₂ 23.972 R4₄₁ −11.0451 mm R4₄₂ 5.799714 mm FOV4 45 TTL4 − SL46.79 mm f4₁ + f4₂ −2.845 Degrees mm f4₂ + f4₄ −14.237 f4₂/f4 −1.044f4₅ + f4₆ 4.836 mm mm V4₁ − V4₂ 32.143 (R4₄₁ − R4₄₂)/( R4₄₁ + R4₄₂)3.211

By the above arrangements of the lenses and stop ST4, the lens assembly4 of the fourth embodiment can meet the requirements of opticalperformance as seen in FIGS. 8A-8C, wherein FIG. 8A shows a fieldcurvature diagram of the lens assembly 4 in accordance with the fourthembodiment of the invention, FIG. 8B shows a distortion diagram of thelens assembly 4 in accordance with the fourth embodiment of theinvention, and FIG. 8C shows a modulation transfer function diagram ofthe lens assembly 4 in accordance with the fourth embodiment of theinvention.

It can be seen from FIG. 8A that the field curvature of tangentialdirection and sagittal direction in the lens assembly 4 of the fourthembodiment ranges from −0.03 mm to 0.05 mm for the wavelength of 0.439μm, 0.546 μm, 0.573 μm, 0.587 μm, and 0.656 μm.

It can be seen from FIG. 8B that the distortion in the lens assembly 4of the fourth embodiment ranges from 0% to 2.0% for the wavelength of0.439 μm, 0.546 μm, 0.573 μm, 0.587 μm, and 0.656 μm.

It can be seen from FIG. 8C that the modulation transfer function oftangential direction and sagittal direction in the lens assembly 4 ofthe fourth embodiment ranges from 0.38 to 1.0 wherein the wavelengthranges from 0.4385 μm to 0.6563 μm, the fields respectively are 0.0000mm, 0.5867 mm, 1.1734 mm, 1.4668 mm, 2.0535 mm, 2.6402 mm, and 2.9335mm, and the spatial frequency ranges from 0 lp/mm to 125 lp/mm.

It is obvious that the field curvature and the distortion of the lensassembly 4 of the fourth embodiment can be corrected effectively, andthe resolution of the lens assembly 4 of the fourth embodiment can meetthe requirement. Therefore, the lens assembly 4 of the fourth embodimentis capable of good optical performance.

Referring to FIG. 9, FIG. 9 is a lens layout and optical path diagram ofa lens assembly in accordance with a fifth embodiment of the invention.The lens assembly 5 includes a first lens L51, a second lens L52, a stopST5, a third lens L53, a fourth lens L54, a fifth lens L55, a sixth lensL56, and an optical filter OF5, all of which are arranged in order froman object side to an image side along an optical axis OA5. In operation,an image of light rays from the object side is formed at an image planeIMA5.

The first lens L51 is a biconvex lens with positive refractive power andmade of plastic material, wherein the object side surface S51 is aconvex surface, the image side surface S52 is a convex surface, and bothof the object side surface S51 and image side surface S52 are asphericsurfaces.

The second lens L52 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S53 is aconcave surface, the image side surface S54 is a concave surface, andboth of the object side surface S53 and image side surface S54 areaspheric surfaces.

The third lens L53 is a biconvex lens with positive refractive power andmade of plastic material, wherein the object side surface S56 is aconvex surface, the image side surface S57 is a convex surface, and bothof the object side surface S56 and image side surface S57 are asphericsurfaces.

The fourth lens L54 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S58 is aconcave surface, the image side surface S59 is a concave surface, andboth of the object side surface S58 and image side surface S59 areaspheric surfaces.

The fifth lens L55 is a meniscus lens with positive refractive power andmade of plastic material, wherein the object side surface S510 is aconcave surface, the image side surface S511 is a convex surface, andboth of the object side surface S510 and image side surface S511 areaspheric surfaces.

The sixth lens L56 is a biconcave lens with negative refractive powerand made of plastic material, wherein the object side surface S512 is aconcave surface, the image side surface S513 is a concave surface, andboth of the object side surface S512 and image side surface S513 areaspheric surfaces

Both of the object side surface S514 and image side surface S515 of theoptical filter OF5 are plane surfaces.

In order to maintain excellent optical performance of the lens assemblyin accordance with the fifth embodiment of the invention, the lensassembly 5 satisfies at least one of the following conditions:

FOV5≤56°  (31)

4 mm<TTL5−SL5<9 mm   (32)

f5₁ +f5₂<−1 mm   (33)

−25 mm<f5₂ +f5₄<−1.5 mm   (34)

−4≤f5₂ /f5≤0   (35)

2 mm<f5₅ +f5₆<35 mm   (36)

25<V5₁ −V5₂<38   (37)

−21.5≤(R5₄₁ −R5₄₂)/(R5₄₁ +R5₄₂)≤3.5   (38)

The definition of FOV5, TTL5, SL5, f5 ₁, f5 ₂, f5 ₄, f5 ₅, f5 ₆, f5, V5₁, V5 ₂, R5 ₄₁, and R5 ₄₂ are the same as that of FOV3, TTL3, SL3, f3 ₁,f3 ₂, f3 ₄, f3 ₅, f3 ₆, f3, V3 ₁, V3 ₂, R3 ₄₁, and R3 ₄₂ in the thirdembodiment, and is not described here again.

By the above design of the lenses, stop ST5, and satisfies at least oneof the conditions (31)-(38), the lens assembly 5 is provided with aneffective shortened total lens length, an effective decreased field ofview, an increased resolution, and an effective corrected aberration.

In order to achieve the above purposes and effectively enhance theoptical performance, the lens assembly 5 in accordance with the fifthembodiment of the invention is provided with the optical specificationsshown in Table 13, which include the effective focal length, F-number,total lens length, field of view, radius of curvature of each lenssurface, thickness between adjacent surface, refractive index of eachlens, Abbe number of each lens, and effective focal length of each lens.Table 13 shows that the effective focal length is equal to 7.0767 mm,F-number is equal to 2.8, total lens length is equal to 7.533 mm, andfield of view is equal to 45 degrees for the lens assembly 5 of thefifth embodiment of the invention.

TABLE 13 Effective Focal Length = 7.076 mm F-number = 2.8 Total LensLength = 7.533 mm Field of View = 45 Degrees Radius of Effective FocalSurface Curvature Thickness Length Number (mm) (mm) Nd Vd (mm) RemarkS51 2.341 2.13 1.535 56.115 4.275 The First Lens L51 S52 −73.615 0.04S53 −351.363 0.48 1.661 28.800 −6.395 The Second Lens L52 S54 4.3 0.31S55 ∞ 0.07 Stop ST5 S56 8.459 1.37 1.661 26.800 8.134 The Third Lens L53S57 −13.970 0.21 S58 −7.870 0.39 1.661 24.700 −9.582 The Fourth Lens L54S59 33.838 0.46 S510 −6.000 0.40 1.661 20.373 27.959 The Fifth Lens L55S511 −4.655 0.24 S512 −6.795 0.50 1.661 20.373 −5.431 The Sixth Lens L56S513 7.905 0.27 S514 ∞ 0.21 1.517 64.167 Optical Filter OF5 S515 ∞ 0.44

The aspheric surface sag z of each lens in table 13 can be calculated bythe following formula:

z=ch ²/{1+[1−(k+1)c ² h ²]^(1/2) }+Ah ⁴ +Bh ⁶ +Ch ⁸ +Dh ¹⁰ +Eh ¹² +Fh ¹⁴+Gh ¹⁶

where c is curvature, h is the vertical distance from the lens surfaceto the optical axis, k is conic constant and A, B, C, D, E, F and G areaspheric coefficients.

In the fifth embodiment, the conic constant k and the asphericcoefficients A, B, C, D, E, F, G of each surface are shown in Table 14.

TABLE 14 Surface k A B C Number D E F G S51 −0.627   3.62E−03 −4.44E−04  2.79E−04 −8.98E−05   0.00E+00   0.00E+00   0.00E+00 S52 0 −1.91E−02  1.44E−02 −4.36E−03   3.99E−04   0.00E+00   0.00E+00   0.00E+00 S53 0−2.79E−04   1.88E−02 −3.93E−03   6.12E−04   0.00E+00   0.00E+00  0.00E+00 S54 14.006 −8.88E−03   1.20E−02 −4.76E−03 −2.79E−03  0.00E+00   0.00E+00   0.00E+00 S56 0 −2.97E−02 −2.54E−02   5.65E−02−2.84E−02 −8.93E−02   1.60E−01 −7.94E−02 S57 0 −1.69E−01   3.93E−02−2.05E−02   1.68E−02   1.44E−02 −5.70E−03 −2.51E−03 S58 24.344 −2.12E−01  1.84E−02   1.70E−02   4.91E−02 −4.10E−03 −2.07E−02   5.78E−03 S59488.898 −2.37E−02   1.75E−02 −8.86E−04 −1.91E−03   1.26E−03 −5.86E−04  1.01E−04 S510 −49.446   3.31E−02   1.62E−02 −2.43E−02   7.66E−03  1.45E−04 −6.97E−04   1.23E−04 S511 −25.672 −6.38E−03   1.08E−02−7.99E−04 −7.18E−04   9.13E−05 −1.66E−05   4.43E−06 S512 −3.722−5.61E−02   1.13E−02   5.35E−03 −9.31E−04 −2.79E−04   4.40E−05  1.08E−06 S513 4.931 −7.33E−02   2.37E−02 −5.01E−03   5.34E−04  8.33E−06 −1.03E−05   7.74E−07

Table 15 shows the parameters and condition values for conditions(31)-(38). As can be seen from Table 15, the lens assembly 5 of thefifth embodiment satisfies the conditions (31)-(38).

TABLE 15 FOV5 45 TTL5 7.533 SL5 2.960 Degrees mm mm f5₁ 4.275 mm f5₂−6.395 f5₄ −9.582 mm mm f5₅ 27.959 f5₆ −5.431 f5 7.076 mm mm mm V5₁56.115 V5₂ 28.800 R5₄₁ −7.870 mm R5₄₂ 33.838 mm FOV5 45 TTL5 − SL5 4.573f5₁ + f5₂ −2.12 Degrees mm mm f5₂ + f5₄ −15.977 f5₂/f5 −0.904 f5₅ + f5₆22.528 mm mm V5₁ − V5₂ 35.74 (R5₄₁ − R5₄₂)/ −1.606 (R5₄₁ + R5₄₂)

By the above arrangements of the lenses and stop ST5, the lens assembly5 of the fifth embodiment can meet the requirements of opticalperformance as seen in FIGS. 10A-10C, wherein FIG. 10A shows a fieldcurvature diagram of the lens assembly 5 in accordance with the fifthembodiment of the invention, FIG. 10B shows a distortion diagram of thelens assembly 5 in accordance with the fifth embodiment of theinvention, and FIG. 10C shows a modulation transfer function diagram ofthe lens assembly 5 in accordance with the fifth embodiment of theinvention.

It can be seen from FIG. 10A that the field curvature of tangentialdirection and sagittal direction in the lens assembly 5 of the fifthembodiment ranges from −0.035 mm to 0.035 mm for the wavelength of 0.436μm, 0.546 μm, 0.573 μm, 0.587 μm, and 0.656 μm.

It can be seen from FIG. 10B that the distortion in the lens assembly 5of the fifth embodiment ranges from −0.8% to 0.2% for the wavelength of0.436 μm, 0.546 μm, 0.573 μm, 0.587 μm, and 0.656 μm.

It can be seen from FIG. 10C that the modulation transfer function oftangential direction and sagittal direction in the lens assembly 5 ofthe fifth embodiment ranges from 0.41 to 1.0 wherein the wavelengthranges from 0.4358 μm to 0.6563 μm, the fields respectively are 0.0000mm, 0.5867 mm, 1.1734 mm, 1.4668 mm, 2.0535 mm, 2.6402 mm, and 2.9335mm, and the spatial frequency ranges from 0 lp/mm to 120 lp/mm.

It is obvious that the field curvature and the distortion of the lensassembly 5 of the fifth embodiment can be corrected effectively, and theresolution of the lens assembly 5 of the fifth embodiment can meet therequirement. Therefore, the lens assembly 5 of the fifth embodiment iscapable of good optical performance.

Referring to Table 16 and Table 17, Table 16 provides opticalspecifications in accordance with a sixth embodiment of the invention;Table 17 provides aspheric coefficients of each surface in Table 16.

The figure which depicts the lens layout diagram of the lens assembly inaccordance with the sixth embodiment of the invention is similar to thefigure which depicts the lens layout diagram of the lens assembly inaccordance with the third embodiment of the invention, thus the figurewhich depicts the lens layout diagram of the lens assembly in accordancewith the sixth embodiment of the invention is omitted.

Table 16 shows that the effective focal length is equal to 7.076 mm,F-number is equal to 2.8, total lens length is equal to 7.7533 mm, andfield of view is equal to 45 degrees for the lens assembly of the sixthembodiment of the invention.

TABLE 16 Effective Focal Length = 7.076 mm F-number = 2.8 Total LensLength = 7.7533 mm Field of View = 45 Degrees Effective Radius of FocalSurface Curvature Thickness Length Number (mm) (mm) Nd Vd (mm) RemarkS61 ∞ −0.346 Stop ST6 S62 2.087953 0.684262 1.535218 56.11525 3.849 TheFirst Lens L61 S63 −154.0975 0.150804 S64 −16.56542 0.324744 1.66134228.8 −5.817 The Second Lens L62 S65 5.076681 0.065043 S66 7.1503391.594457 1.661342 26.8 5.011 The Third Lens L63 S67 −3.914118 0.029974S68 −5.237808 1.100006 1.661342 24.7 −7.414 The Fourth Lens L64 S6989.06507 0.041966 S610 26.85975 1.238261 1.662342 20.3729 29.636 TheFifth Lens L65 S611 −72.18347 0.678644 S612 −13.26351 0.499951 1.66134220.3729 −3.702 The Sixth Lens L66 S613 3.062019 0.27 S614 ∞ 0.21 1.516864.16734 Optical Filter OF6 S615 ∞ 0.437948

The aspheric surface sag z of each lens in table 16 can be calculated bythe following formula:

z=ch ²/{1+[1−(k+1)c ² h ²]^(1/2)}+Ah⁴ +Bh ⁶ +Ch ⁸ +Dh ¹⁰ +Eh ¹² +Fh ¹⁴+Gh ¹⁶

where c is curvature, h is the vertical distance from the lens surfaceto the optical axis, k is conic constant and A, B, C, D, E, F and G areaspheric coefficients.

In the sixth embodiment, the conic constant k and the asphericcoefficients A, B, C, D, E, F, G of each surface are shown in Table 17.

TABLE 17 Surface K A B C Number D E F G S62 0 0.00E+00 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 S63 0 0.00E+00 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 S64 0 0.00E+00 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 S65 0 0.00E+00 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 S66 0 0.00E+00 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 S67 3.341941 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 S68 0 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 S69 0 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 S610 0 0.00E+00 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 S611 −21025.33 0.00E+000.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 S612 36.540960.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 S613−0.898173 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00

The difference between the above sixth embodiment of the lens assemblyand the third embodiment of the lens assembly is that the image sidesurface S63 of the first lens L61 is a convex surface for the sixthembodiment of the lens assembly, however, the image side surface S33 ofthe first lens L31 is a concave surface for the third embodiment of thelens assembly.

The above field curvature (figure is omitted) and distortion (figure isomitted) for the sixth embodiment of the lens assembly can be correctedeffectively, and the resolution for the sixth embodiment of the lensassembly can meet the requirement. Therefore, the lens assembly of thesixth embodiment is capable of good optical performance.

While the invention has been described by way of example and in terms ofthe preferred embodiment(s), it is to be understood that the inventionis not limited thereto. On the contrary, it is intended to cover variousmodifications and similar arrangements and procedures, and the scope ofthe appended claims therefore should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements and procedures.

What is claimed is:
 1. A lens assembly comprising: a first lens which iswith positive refractive power and comprises a convex surface facing anobject side; a second lens which is with negative refractive power andcomprises a concave surface facing an image side; a third lens which iswith refractive power and comprises a convex surface facing the imageside; and a fourth lens which is with refractive power; wherein thefirst lens, the second lens, the third lens, and the fourth lens arearranged in order from the object side to the image side along anoptical axis; wherein the lens assembly satisfies:FOV≤56°, wherein FOV is a field of view of the lens assembly.
 2. Thelens assembly as claimed in claim 1, wherein the third lens is withnegative refractive power and the fourth lens is with positiverefractive power.
 3. The lens assembly as claimed in claim 1, whereinthe first lens further comprises a concave surface facing the imageside, the second lens further comprises a convex surface facing theobject side, the third lens further comprises a concave surface facingthe object side, and the fourth lens comprises a convex surface facingthe object side and a concave surface facing the image side.
 4. The lensassembly as claimed in claim 1, wherein the first lens further comprisesa concave surface facing the image side, the second lens furthercomprises a convex surface facing the object side, the third the fourthlens comprises a convex surface facing the object side and a convexsurface facing the image side.
 5. The lens assembly as claimed in claim1, wherein the lens assembly satisfies:−21.5≤(R ₄₁ −R ₄₂)/(R ₄₁ +R ₄₂)≤3.5, wherein R₄₁ is a radius ofcurvature of an object side surface of the fourth lens and R₄₂ is aradius of curvature of an image side surface of the fourth lens.
 6. Thelens assembly as claimed in claim 1, further comprising a stop disposedbetween the object side and the third lens, wherein the lens assemblysatisfies:4 mm<TTL−SL<9 mm, wherein TTL is an interval from the convex surface ofthe first lens to an image plane along the optical axis and SL is aninterval from the convex surface of the first lens to the stop along theoptical axis.
 7. The lens assembly as claimed in claim 1, wherein thelens assembly satisfies:f ₁ +f ₂<−1 mm, wherein f₁ is an effective focal length of the firstlens and f₂ is an effective focal length of the second lens.
 8. The lensassembly as claimed in claim 1, wherein the lens assembly satisfies:−4≤f ₂ /f≤0, wherein f₂ is an effective focal length of the second lensand f is an effective focal length of the lens assembly.
 9. The lensassembly as claimed in claim 1, wherein the lens assembly satisfies:25<V ₁ −V ₂<38, wherein V₁ is an Abbe number of the first lens and V₂ isan Abbe number of the second lens.
 10. The lens assembly as claimed inclaim 1, wherein the lens assembly satisfies:−25 mm<f ₂ +f ₄<−1.5 mm, wherein f₂ is an effective focal length of thesecond lens and f₄ is an effective focal length of the fourth lens. 11.A lens assembly comprising: a first lens which is with positiverefractive power and comprises a convex surface facing an object side; asecond lens which is with negative refractive power and comprises aconcave surface facing an image side; a third lens which is withrefractive power and comprises a convex surface facing the image side; afourth lens which is with refractive power; a fifth lens which is withrefractive power; and a sixth lens which is with refractive power;wherein the first lens, the second lens, the third lens, the fourthlens, the fifth lens, and the sixth lens are arranged in order from theobject side to the image side along an optical axis; wherein the lensassembly satisfies:2 mm<f ₅ +f ₆<35 mm, wherein f₅ is an effective focal length of thefifth lens and f₆ is an effective focal length of the sixth lens. 12.The lens assembly as claimed in claim 11, wherein the third lens is withpositive refractive power, the fourth lens is with negative refractivepower, the fifth lens is with positive refractive power, and the sixthlens is with negative refractive power.
 13. The lens assembly as claimedin claim 11, wherein the second lens further comprises a concave surfacefacing the object side, the third lens further comprises a convexsurface facing the object side, the fourth lens is a biconcave lens, thefifth lens comprises a convex surface facing the object side, and thesixth lens is a biconcave lens.
 14. The lens assembly as claimed inclaim 11, wherein the second lens further comprises a concave surfacefacing the object side, the third lens further comprises a convexsurface facing the object side, the fourth lens is a biconcave lens, thefifth lens comprises a concave surface facing the object side, and thesixth lens is a biconcave lens.
 15. The lens assembly as claimed inclaim 13, wherein the lens assembly satisfies:−21.5≤(R ₄₁ −R ₄₂)/(R ₄₁ +R ₄₂)≤3.5, wherein R₄₁ is a radius ofcurvature of an object side surface of the fourth lens and R₄₂ is aradius of curvature of an image side surface of the fourth lens.
 16. Thelens assembly as claimed in claim 12, further comprising a stop disposedbetween the object side and the third lens, wherein the lens assemblysatisfies:4 mm<TTL−SL<9 mm, wherein TTL is an interval from the convex surface ofthe first lens to an image plane along the optical axis and SL is aninterval from the convex surface of the first lens to the stop along theoptical axis.
 17. The lens assembly as claimed in claim 16, wherein thelens assembly satisfies:f ₁ +f ₂<−1 mm, wherein f₁ is an effective focal length of the firstlens and f₂ is an effective focal length of the second lens.
 18. Thelens assembly as claimed in claim 16, wherein the lens assemblysatisfies:−4≤f ₂ /f≤0, wherein f₂ is an effective focal length of the second lensand f is an effective focal length of the lens assembly.
 19. The lensassembly as claimed in claim 12, wherein the lens assembly satisfies:25<V ₁ −V ₂<38, wherein V₁ is an Abbe number of the first lens and V₂ isan Abbe number of the second lens.
 20. The lens assembly as claimed inclaim 15, wherein the lens assembly satisfies:−25 mm<f ₂ +f ₄<−1.5 mm, wherein f₂ is an effective focal length of thesecond lens and f₄ is an effective focal length of the fourth lens.